Methylmercury movements across the perfused guinea pig placenta in late gestation

Abstract

Placentas from guinea pigs between 61 and 63 days gestation were perfused from the fetal side in situ at rates ranging from 0.35 to 4.54 ml/min. The dam was injected intravenously with tracer quantities of tritiated water and radiolabeled mercury in the form of methylmercuric chloride. Maternal plasma and the perfusate samples were analyzed for radiolabeled mercury and tritiated water, and corrections were made for net water flows by using radioiodinated serum albumin. Radiomercury and tritium clearances were therefore measured concurrently. The clearance of tritiated water was a linear function of perfusion rate. The relationship between tritium clearance and perfusion rate for all experiments combined was described by the equation: y = 0.16 + 0.54 x, where y is tritium clearance and x is perfusion rate. Clearance of radiolabeled mercury measured 0.15 ± 0.01 ml/min (mean ± SE). No significant relationship between radiomercury and tritium clearance was detected. It appears that calcium and low concentrations of methylmercury may move across the placenta by the same or similar mechanisms.